Fibrosis is characterized by excessive production and accumulation of extracellular matrix proteins, which leads to progressive loss of tissue function and eventual organ failure. Chronic kidney diseases, irrespective of primary insults, are usually accompanied by kidney interstitial fibrosis. Therapeutic strategy for chronic kidney disease, in order to halt decline of kidney function, requires not only removal of the causal factors, such as hyperglycemia, hypertension, and HIV infection, but also anti-fibrosis therapy to restore the normal kidney structure and function.
Transforming growth factor-β1 (TGF-β1) has been identified to be the most important pro-fibrogenic factor for kidney disease. TGF-β1 binds to type II TGF-β receptor, allowing its dimerization with type I TGF-β receptor and leading to phosphorylation of Smad2 and Smad3. Phosphorylated Smad3 relocates into nuclei, thereby binds to Smad binding element in promoter and activating the transcription of the target genes including pro-fibrotic genes such as collagen I, fibronectin, and alpha-smooth muscle actin (α-SMA). It is known that Smad3 is highly activated in fibrotic kidney and that knockout of Smad3 attenuates kidney fibrosis in animal models of kidney disease. Blockade of TGF-β1/Smad3 pathway therefore provides a therapeutic strategy for kidney fibrosis.